Devices for treating a part of a body of a person, for example by cutting hair on a part of a body to be treated, include powered hand-held devices, for example a trimmer, that are placed against a part of a user's body and moved over and/or aligned with areas where hair is to be cut. Such devices include mechanical hair cutting devices. The user may trim a hairline, for example a neckline or sideburns, by moving and positioning a cutting unit, for example a cutting blade, with respect to the part of the body and moving the cutting unit appropriately.
However, when cutting a user's own hair, or someone else's hair, significant skill is required to provide a presentable result. Such devices are difficult to accurately position on a user's head, for example. The accuracy of the treatment provided by the device depends on the user's skill and steady hand. Moreover, the device and the user's hand and arm may impede the user's view thereby making it difficult to position and orientate the device accurately.